Study of the hydrodynamic performance of impermeable and permeable breakwaters using Smoothed Particle Hydrodynamic

Sloping coastal structures such breakwaters, are the most common structures that used near shore. Breakwaters are generally constructed to protect vessels, facilities, and coastal buildings against wave erosion and attack. Different materials such as concrete or large rock are used to construct these structures. Design of breakwater includes both hydraulic and structural aspects. During physical process, wave run-up is one of the important parameters in the hydraulic design that control the crest level of these structures. However, prediction of wave run-up has not yet fully understood and therefore, research study on different types and scale of breakwater is going on. A large number of experimental and field studies have been performed in this regard. However, scale effect in experimental measurement and cost in field study are the main disadvantages of these methods. By computational improvement, numerical methods have gradually been applied to model waves around breakwaters in one, two and three dimensions. These techniques can generally be classified into mesh-based and mesh-free categories which can be implemented in an Eulerian and/or a Lagrangian frame. Although traditional mesh-based methods (such as finite differencing (FDM), finite element (FEM) and finite volume (FVM)) have been applied in this area, they face many difficulties such as mesh dependency, large deformation or fragmentation, accurate tracking of the free-surface, modeling movable boundaries, and uniform mesh generation for complicated geometries. In order to overcome difficulties and limitations that associated with traditionally Mesh-based methods, next generation of numerical methods namely mesh-free methods have been gradually applied in fluid mechanics. Among these techniques, smooth particle hydrodynamics (SPH), with a Lagrangian frame, has been claimed to be one of the most powerful methods for modeling broad range of complex hydrodynamic phenomena. SPH was originally developed in the late 1970s for astrophysical applications and was later applied to solid mechanics. The capability of SPH in capturing large deformations led to its subsequent application to simulate some free-surface flows such as modeling of wave reflection and transmission at permeable or impermeable breakwaters. This research aims to apply 2D weakly compressible SPH to Rigid breakwater in multi slope bed, and evaluate the hydraulic performance resulting from the interaction of water waves on impermeable and non-overtoppable type of breakwater and insight into this powerful method for coastal structures using SPHysics. Effect of different parameters such as variation in still water depth, wave period, wave steepness, side slope of breakwater on the wave run-up is investigated. Additionally, in order to compare the wave run-up on rubble mound breakwater, simulation results using SPH have been compared with experimental work. The continuity and momentum equations in a 2-D Lagrangian frame and linearized version of the state equation were used to model viscous, weakly compressible and baratropic fluid around breakwater. To solve these nonlinear equations using SPH, the B-Spline kernel function is used during modeling. Moreover, the radius of the support domain was taken as 1.2 times the initial particle distance and Linked-list method is used for search algorithm in the numerical method. Solid boundaries such as walls are represented by dummy particles using two set of virtual particles. To model wave run-up problem, piston type wave maker is located at the end of a long rectangular tank which is oscillated with prescribed frequency. A tank with initial height and length equal to 0.2 and 4 m, respectively, was considered. A wave with different period (Ti=1.273s, 1.626s, 1.979s) and depth (di= 0.48m, 0.51m, 0.54m) was generated using piston type wave maker. Additionally, various slope of breakwater (cot α=1.25, 2, 2.5) and slope of sea bed (0.382, 1.1460) was considered. As a consequence, run up which has a crucial role in design of breakwaters was grown by increasing of period, depth and slope of breakwater. The satisfactory agreement between SPH results and the USBR experimental data showed that this numerical technique is capable of handling wave run-up on rigid breakwater. Further, due to investigate wave run-up rate on impermeable and rubble mound breakwaters, numerical results of this study is compared with experimental measurements by shirian, Shankar and Jayaratne. Similar tendency of wave run-up with variation of side slope of breakwater and wave period is observed. However, wave run-up on impermeable breakwaters is higher (approximately 40%) than rubble mound types.